GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA 



great taxonomic importance, but in combination with 

 the peculiarities of the dorsal valve form a unique 

 ensemble. The structure of the cardinalia is compar- 

 able to that of Orthorhynchula among the early Rhyn- 

 chonellacea, is much simpler than in the Pentameridae, 

 but not more so than in the Camerellidas. In Ortho- 

 rhynchula the crural bases are concave plates hanging 

 free in the valve and bear long, curved crural processes. 

 Regarding Stricklandia, Hall and Clarke have this 

 to say: 



These pentameroids are principally remarkable for the 

 unusual development of the cardinal areas of both valves 

 in the larger and more typical species, and the straight 

 orthoid hinge in the earlier and smaller members of the 

 group. The combination of such features with an internal 

 chambered structure is not of frequent occurrence among 

 these genera. [The interareas] are sharply defined on both 

 valves, and so persistent are they that we look for the origin 

 of this combination, not among the various pentameroids. . . 

 but to the small, transverse shells of the early faunas to 

 which the term Syntrofhia has been applied, 



as Syntrofhia ? arachne and S. ? arethusa of the Lower 

 Ordovician; these species, however, are not of the 

 genus Syntrofhia but may belong to Huenella. This 



origin may not be the correct one, but in that event 

 why do we not find any Ordovician stricklandid ? We 

 are therefore inclined to look for the origin of the 

 family in the Camerellidae, with the idea that the 

 small inherited interareas are redeveloped into the 

 much larger ones of Stricklandia. 



In the dorsal valve of Stricklandia, according to 

 Hall and Clarke, "the short dental plates, at their 

 inner angles, bear long crural processes," and are 

 analogous with those of Amfhigenia, but do not unite 

 to form a hinge-plate or cruralium as in that genus. 

 On page 355 these authors erect the family Strick- 

 landidas for the genera Syntrofhia and Stricklandia. 

 The present authors agree that Stricklandia can not be 

 incorporated in the family Pentameridae, and we there- 

 fore accept the family Stricklandids but exclude from 

 it Syntrofhia.^^ 



^' The junior author would exclude the Stricklandid^ 

 from the Pentameroidea entirely. The cardinalia are 

 totally unlike anything known in that order (Syntrophiacea 

 and Pentameracea). In his opinion the best place for 

 Stricklandia, so far as present knowledge goes, is among the 

 early RhynchoneUacea. 



